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J  COMPARATIVE  VALUE  OF  EXPERIMENTS  ON  DIFFERENT 
LABORATORY  ANIMALS 
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Contradictory  statements  have  frequently  been  made  with  regard 
to  efficiency  of  different  compounds  used  for  the  treatment  of  experi¬ 
mental  trypanosomiasis.  This  is  due,  to  a  great  extent,  to  the  species 
of  animal  used  for  the  experiments  and  to  the  virulence  of  the  strain 
of  trypanosomes  employed.*  Small  laboratory  animals,  as  mice,  rats, 
guinea-pigs  and  rabbits  react  in  different  ways  to  infection  with 
trypanosomes  and  also  towards  drugs.  The  most  conclusive  results 
are  obtained  by  using  rats,  as  these  animals  are  very  susceptible  to 
infections  with  trypanosomes,  and  their  reaction  is  very  constant. 
The  relapsing  time  is  fairly  regular  and  in  direct  proportion  to  the 
trypanocidal  action  of  different  compounds. 
Guinea-pigs  are,  as  Uhlenhuth,  Htibner  and  Woithe  and  ourselves 
have  pointed  out  before,  very  disappointing,  in  so  far  as  these  animals 
very  often  die  after  a  short  course  of  treatment  for  no  apparent  reason. 
Rabbits,  too,  are  only  to  a  certain  extent  reliable.  The  infection  is 
of  a  chronic  character,  and  parasites  are  usually  present  in  an 
exceedingly  small  number.  Symptoms,  such  as  inflammation  of  the 
eyelids,  swelling  of  the  ear  and  nose,  although  well  marked,  are 
generally  easily  controlled  by  the  different  trypanocidal  drugs. 
It  is  unsafe  to  draw  general  conclusions  from  experiments  with 
mice,  for  the  use  of  drugs  in  the  treatment  of  Sleeping  Sickness  and 
cattle  trypanosomiasis,  as  mice  tolerate  in  proportion  to  the  body 
weight  immense  doses  of  different  drugs.f 
Changes  of  virulence  have  been  noted  on  a  few  occasions  in  the  case  of 
7’.  gambiense.  On  one  occasion  T .  gambiense  was  recovered  from  the  blood  of  a 
monkey  at  the  time  of  a  relapse,  after  a  prolonged  negative  interval.  The  number 
of  parasites  in  the  blood  of  the  monkey  increased  very  rapidly  within  two  days  and 
killed  the  animal.  On  subinoculation  into  rats  it  was  noticed  that  these  animals 
succumbed  to  the  infection  usually  within  3  to  4  days.  After  a  passage  through 
guinea-pigs  the  heightened  virulence  of  the  strain  was  lost,  and  it  killed  rats  again 
in  the  normal  period,  namely  40-120  days. 
t  Compare  the  following  table  from  Kohl’s  publication.  (Zeitschrift  f. 
Tmmunitatsforschung,  Kd.  T,  p.  634.)  The  maximal  dose  pro  Kg.  body  weight: — 
Mouse 
Atoxyl. 
o‘  1 7  gm . 
Arseno-phenyl-glycinf. 
0*6  gm. 
Rat 
o'lygm. 
... 
.  0-4  gm. 
Guinea-pig 
o'oSgm. 
.  .  . 
...  ...  o'i2gm. 
Rabbit 
0-07  gm. 
0'22gm. 
Dog  . 
o’oi  gm. 
o'2gm. 
Horse 
.  0-075  gm. 
